1. Field of the Invention
The present invention relates to a silicone resin composition, a silicone resin sheet, a method for producing a silicone resin sheet, and an optical semiconductor device. In particular, the present invention relates to an addition cure type silicone resin composition; a silicone resin sheet composed of the silicone resin composition; a method for producing the sheet; and an optical semiconductor device in which the sheet is used for encapsulation.
2. Description of Related Art
High output white LED devices which has been examined for general light application are required to have an encapsulating material that has excellent light resistance and heat resistance, and recently, so called “addition cure type silicone” is widely used. The addition cure type silicone is obtained by allowing a mixture mainly composed of a silicone derivative having a vinyl group in its main chain and a silicone derivative having a hydrosilyl group (SiH group) in its main chain to thermally cure in the presence of a platinum catalyst, and examples thereof are disclosed in Japanese Unexamined Patent Publication No. 2000-198930, Japanese Unexamined Patent Publication No. 2004-186168, and Japanese Unexamined Patent Publication No. 2008-150437.
As a method for encapsulating an LED element using such an addition cure type silicone, because the addition cure type silicone is liquid before curing, preferably, a “potting” method is used: in the potting, a cup in which an LED element is disposed is filled with a resin, and thereafter curing by heat is carried out.
However, in the method, when producing a chip array module, which is recently becoming a mainstream production, and in which a plurality of LED elements are disposed on a substrate, the height of the encapsulating resin are varied due to sagging, which causes insufficient optical characteristics in the obtained LED device. Also, viscosity of the resin before being cured easily changes depending on the environment that surrounds the resin, and therefore there are disadvantages such as poor productivity because of such unstable potting conditions.
In contrast, a method in which an LED element is encapsulated using a sheet resin is proposed. For example, in Japanese Unexamined Patent Publication No. 2007-123452, an encapsulating sheet composed of an ethylene-vinyl acetate polymer and polyurethane is disclosed, and in Japanese Patent No. 4383768, an encapsulating sheet composed of a crosslinkable thermoplastic resin of an ethylene(meth)acrylate copolymer is disclosed. Furthermore, in Japanese Unexamined Patent Publication No. 2009-84511, an encapsulating sheet composed of a thermosetting silicone resin and a thermoplastic silicone resin is disclosed.